1. Field of the Invention
The invention relates to a device for protecting electronic equipment against strong electromagnetic pulses. It is an object of the device according to the invention to give protection against intense electromagnetic pulses, such as those produced by lightning. A fortiori, the device according to the invention can be used for protection against a less intense electromagnetic perturbation.
2. Discussion of Prior Art
In general it may be considered that disturbances to electronic eqiupment are due to two causes, on the one hand the direct coupling of an electromagnetic field with the electronic equipment, and on the other hand injection via connections (communication, electric supply, . . . ) associated with such equipment. The injection itself is due to the coupling between the electromagnetic field and the connection.
Direct coupling between the electromagnetic field and the electronic equipment can be eliminated in known manner by disposing the electronic equipment to be protected in a radioelectrically protected enclosure (Faraday cage). However, such protection is inadequate if the electronic equipment disposed in the Faraday cage is connected to other equipment outside the cage via an unprotected connection.
The injection of an electromagnetic pulse into the connection results in a stray voltage and/or current pulse of very high maximum value. In the case of lightning, the voltage may reach 10 kV and the intensity 20 kA. Such a pulse propagated over a connection reaches the equipment at an input where it normally receives a signal of much lower voltage, of the order of 500 volts for an electric supply connection and a few tens of volts for a telephone or digital connection. Such a pulse is therefore highly liable to damage the electronic equipment very seriously.
The prior art, more particularly French Patent 2563058, filed in the Applicants' name on Apr. 17, 1984, discloses a device for protecting electronic equipment against strong electromagnetic pulses. The device is disposed between a connection and the equipment to be protected. The device comprises a non-linear element of clipper type to divert the maximum intensity of the electromagnetic pulse from the connection to ground, and a filtering means also for drawing off current and/or energy not diverted after clipping, but also for attenuating the voltage level of the pulse after clipping.
The device gives protection against intense electromagnetic pulses whose rising front is very fast, such as an impulse caused by lightning.